1. Field of the Invention
This invention relates generally to crop canopy light sensors and, more specifically, to an algorithm and method for the real-time application of agrochemicals utilizing active crop-canopy light sensors.
2. Background of the Art
The term “precision farming” is often used to describe the management of spatial variability in soil and crop conditions within a field. Other terms, “site specific farming”, “prescription farming”, and “variable rate application (VRA) technology” are sometimes used synonymously with precision farming to describe the tailoring of soil and crop management to the conditions at various locations throughout a field. Typical precision farming techniques include: varying the planting density of individual plants based on the ability of the soil to support growth of the plants; and the selective application of farming products such as herbicides, insecticides, and, of particular interest, fertilizer. Precision farming techniques utilizing, for example, Global Positioning System (GPS) technology has found many uses, one being the application of fertilizers in agricultural fields, as is described, for example, in U.S. Pat. No. 5,220,876 to Monson et al. The '876 patent describes a variable-rate fertilizer application system. The system has a digital map characterizing the field's soil types. The system also has other maps that characterize the desired level of various fertilizer types to be applied upon the field. The patent states that the levels of fertilizer can be determined from predefined characteristics, such as existing fertilizer levels, field topography or drainage studies. A processor calculates and controls the dispensing of the various fertilizers based on both the soil map and the fertilizer map. A position locator on the vehicle dispensing the fertilizers provides the necessary location information to apply the prescribed amount of fertilizer in the correct location. Related U.S. Pat. No. 5,355,815 to Monson describes a closed-loop fertilizer application system, which also varies the application rate, but which does not require maps of current fertilizer levels. The system is said to be able to determine a chemical prescription in real-time for a soil scene, depending on the existing soil fertilizer content ascertained by a real-time soil analyzer.
Another variable-rate fertilizer application system is described in U.S. Pat. No. 4,630,773 to Ortlip. The '773 patent describes a system that applies fertilizer according to the specific needs of each individual soil type of soil comprising a field. The patent also describes the assembly of a digital soil map for a field to be fertilized. An aerial infrared photograph of the field is taken. The patent states that the different shades in the photograph correspond to different moisture contents of the soil types. The photograph is digitized into an array of pixels. Each pixel is assigned a digital value based on the shading in the photograph, such that the value is representative of the soil type the pixel represents. The application of fertilizer is varied according to the digital soil map.
U.S. patent application Ser. No. 11/085,589 and U.S. Pat. Nos. 6,889,620 and 7,171,912 utilize maps of site-specific amounts of a soil nutrient, to be applied in fertilizer to an agricultural field is created using a map of site-specific amounts of the soil nutrient needed to produce the maximum possible yield at the particular site. The nutrient amounts may be added to the soil using the map and conventional variable-rate fertilizer application methods. In one embodiment, the amounts of the soil nutrient needed to produce the maximum possible yield at each site is created using a map of site-specific measures of biomass produced by the field in a past growing season or seasons, which in turn is created from a remotely sensed biomass image.
U.S. Pat. No. 6,393,927 discloses a method and apparatus for the real time determination and application of optimum amounts of nitrogen fertilizer to corn and other arable crops such as cotton, sugar beats, wheat, etc. by the use of rapid, non-destructive sensors and various fertilizer application methods. In a first embodiment, optical reflectance measurements of the crop canopy and a reference strip at the fertilizer response plateau are taken by sensors carried by a center pivot irrigation system. A second embodiment of the invention utilizes a tractor drawn fertilizer applicator with the sensors mounted on the application booms. This second embodiment may also utilize the Global Positioning System to provide tractor position for storage along with crop data for later use and comparison.
U.S. Pat. Nos. 6,601,341, 6,880,291 and 7,188,450 disclose methods for in-season macro and micronutrient application based on predicted yield potential and a nutrient response index. U.S. Pat. Nos. 6,601,341 and 6,880,291 disclose methods that include the steps of: determining a nutrient response index for a field; determining the normalized difference vegetation index (NDVI) of an area to fertilize; determining a predicted crop yield for the area; determining an attainable crop yield for the area; determining the nutrient requirement for the area as the difference between the nutrient removal at the attainable yield minus the nutrient removal at the predicted yield, adjusted by the efficiency of nutrient uptake in the particular crop. Whereas the U.S. Pat. No. 7,188,450 method includes the steps of: determining a nutrient response index for a field; determining the NDVI of an area to fertilize; determining the coefficient of variation of NDVI over a plot; determining a predicted crop yield for the area without additional nutrient; determining an attainable crop yield for the area with additional nutrient; determining the nutrient requirement for the area as the difference between the nutrient removal at the attainable yield minus the nutrient removal at the predicted yield, adjusted by the efficiency of nutrient utilization in the particular crop as indicated by the coefficient of variation. Like the '927 patent, both methods rely on a producer-created adequately fertilized reference area in order to calibrate the sensing system to field growing conditions.
There are many problems associated with utilizing a high N reference strip or region as an in-season calibration standard for calibrating real-time remote sensors. The reference concept assumes that a section of the field (usually a strip) can be over fertilized so as to create a region in the field that is non nutrient limited. The region can then be compared to the remainder of the field in order to determine the site specific nutrient needs for the entire field. It is assumed that if a non treated portion of the field compares in biomass and/or color (dark green) to the reference strip, then it has its nutrient requirements met and subsequently will receive less nutrient via variable rate application. Whereas, portions of the field that have lower biomass and/or lighter color (pale green) in comparison to the reference strip receive higher amounts of nutrient. If fields had uniform soil, drainage, micronutrients, organic matter, etc. . . . the reference strip concept would be and exceptional solution for in-season, real-time variable rate applicator calibration. Herein lays the primary problem: crops grown within a reference strip in the real world can not be an absolute reference for comparison to crops grown in other locations in the field. This is due to crop growth variability resulting from variable soil types throughout the field. Variations in organic matter, micronutrients and drainage impact how the crop will grow. Even within the reference strip, wide variations in crop status can be measured as the reference strip transverses the various soil types and conditions across the field, see FIG. 1. Here, notice the spatial variability apparent in each of the three preplant N rates, especially notice the variations in the 252 kg/ha reference strip rate. As such, data collected from the reference strip crops can result in a dubious standard for comparison against crops grown in other regions of the field. Varying levels of organic matter and resulting mineralization can give a false indicator as to plant's future nutrient requirements, that is, a plant can appear to have adequate nutrient resources when compared to the reference plants. In reality, available soil nutrient may be on the verge of running out and subsequently these plants would be deprived of required nutrients as the plant accumulates biomass later in the growing season.
Another problem related to the use of the reference strip concept pertains primarily to adoption by the end user. Cultural practice barriers are difficult to over come. Many growers do not want the added steps and cost of preparing and managing a nutrient rich reference region in their fields. A University of Nebraska extension publication actually recommends not just one reference strip per field but rather several. Furthermore, many large growers may have up to a dozen fields to manage each with multiple reference strips. Sprayer service companies may have dozens of fields to manage for their clients. In addition to establishing a reference strip in a particular field, care has to be exercised as to where the reference strip is positioned within a field from year-to-year. Reference strip management is not a management process that is desirable for growers to adopt. Conceptually, the use of a reference strip or region appears to be a novel method to calibrate remote sensing instrumentation, however, when one considers management overhead involved, the appeal of the technique quickly fades as the management and logistical realities become clear.
In the following, we will disclose an alternative method that uses real-time active crop sensors for variable rate control of agrochemicals. The method to be presented differs from previous VRA systems in that it does not require the use of a managed crop reference strip or region in a field to calibrate the system and it does not rely on preprocessed geospatial, yield or biomass data in order to make agrochemical rate prescriptions.